I believe that my 02 ford explorer is cooling system problem. Noticed car has been hard to start the last few days but ONLY WHEN HOT. I usually watch my gauges regularly and I noticed the coolant temp gauge bounce once or twice then drop. (To the cold end and not move) I thought I might be low on coolant and the ECT sensor wasn't registering. Checked the resevoir and sure enough it was empty. Filled coolant resevoir and started car to see if coolant would get sucked into engine, and see if temp gauge moves. After a short ride to get engine temp up gauge would still not move. But car is experiencing overheating symptoms. Increased idle speed and hard to start when hot. fan clutch seems ok, no leaks in radiator that I can see. No coolant in oil that I can tell. Upper radiator hose gets hot and pressurized. but gauge is still not registering. Does this sound like a thermostat ?
If the level was low you probably have air in the system. And for it to be low its gotta be going somewhere
Increased idle speed in normal when the engine is cold. The purpose is to being the engine up to operating temperature. It should automatically slow down after it heats up.
If there was no coolant in the recovery tank you either have a leak somewhere or the cap on the tank is faulty and will not hold pressure. If the cap does not hold pressure the cooalt will eventually loose pressure. I had the same problem with a 2003. Small loss of coolant over a period of time but no obvious leak. Here is what I did and I discovered the leak. Obtain a radiator pressure tester from Autozone, or the like, and screw on the proper fitting on the recovery tank. Pump the system up to fifteen pounds and let it sit. (cold engine please). Mine was leaking ever so slightly from the thermostat housing (V6) under pressure. The housing is made of plastic (why I do not know) and the metal insert inside the housing goes bad causing a small leak under pressure where the pieces are sandwiched together. The part is about ninty bucks and can be changed by removing the upper radiator hose, the diverter hose to the heater, and three 10 or 8 mm bolts which attached the housing to the top of the manifold. Takes about ten minutes on a cool engine. The termostat comes with the part, so resist the urge to unscrew the cover and look at the thermostat. When under fifteen pounds of pressure the housing leaked like anything. Because of it's location, when it leaks it falls on the manifold then down the block. The leak is so small there was no evidence on the ground because the coolant would evaporate before dripping on the ground.
Correction: If the cap does not hold pressure, the coolant will eventually evaporate out of the system.
Just adding coolant to an empty overflow tank will not always put it back in radiator. Must belch system to insure that radiator and block are full of coolant. Sounds like your system is very low on coolant. Might not show actual engine temp if no coolant is actually making it to temp sensor. Cannot stress enough to double check that block and radiator is completely full.
Dadyoun: How would you belch the system on a 2002 Explorer? The recovery tank is the only place coolant can be added. Inasmuch as the recovery tank is about eight inches above the manifold, gravity and water seeking its level should fill the system almost full. Of course you have to run the engine to get it up to temp so the thermostat will open and begin the flow of coolant back to the radiator.
Sorry was thinking that one had a petcock to release trapped air.
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